1. Field of the Invention
The present invention relates to a method of charging a vertical tube with catalyst particles. Such catalyst-filled tubes are employed for carrying out various catalytic gas-phase reactions. Depending on the type of catalyzed reaction, the tubes are heated from the outside or are surrounded by a heat transfer medium such as a salt melt to remove heat. The catalyst particles either consist of a catalytically active composition which has been shaped, with or without use of suitable binders, by extrusion, tableting or the like to give shaped bodies (all-active catalysts) or they comprise a catalytically active composition which is applied in the form of a shell to an inert support (coated catalysts). They can be in the form of spheres, rings, cylinders, cubes, cuboids, or other geometric bodies.
2. Description of the Related Art
When the catalyst particles are introduced into the tube, catalyst particles can break or the catalytic active composition can be partly detached from the support as a result of mechanical stress, depending on the lateral compressive strength and the fracture strength of the catalysts used. The fragments or abraded material formed increase the density of the catalyst bed and during later operation of the tube reactors lead in a disadvantageous fashion to increased pressure drops.
It has therefore been proposed that the speed at which the catalyst particles fall during introduction into the tube be reduced by use of particular filling aids. Thus, EP-A 548 999 describes a method of charging tubes in which the catalyst particles are introduced along a string having flexible bristles which extend in the transverse direction and are located at a distance from one another.
A further method of introducing catalyst particles into a tube is described in U.S. Pat. No. 3,608,751. The filling aid used here is a flexible body, e.g. a hemp rope, to which oblique blades are affixed.
Although the known methods are well-suited to filling steam reformer tubes which typically have an internal diameter of about 10 cm, they are unsuitable for tubes having smaller internal diameters, as are customarily used for exothermic gas-phase reactions, in particular gas-phase oxidations. Just the introduction of the string bearing bristles or blades into a narrow tube is much more difficult. In addition, the bristles or blades of the known filling aids quickly lead to blocking of the tube or enmeshing of the catalyst particles in the case of small tube diameters.
It is an object of the present invention to provide a method by means of which vertical tubes having a small tube diameter, as are used for gas-phase oxidation reactions, can be charged with catalyst particles while avoiding, firstly, catalyst fracture or abrasion and, secondly, blockages and enmeshing of the catalyst particles.